The present invention relates to clean rooms and, more particularly, to filter units supportable in a ceiling or wall gridwork adjacent a clean work area.
In the manufacture of semiconductor chips, electronic components, pharmaceuticals and in the performance of certain surgical procedures, it is necessary or desirable to control the environmental conditions within the work area, especially dust conditions. Such controlled work areas are commonly called clean rooms.
In one typical type of clean room construction, the ceiling of the room includes a plurality of side-by-side air filtration or diffuser units. Each of the units includes an individual hood or air plenum with a high-efficiency filter positioned across the opening thereof at or near the clean room surface. Air is pumped into each plenum and through each filter, the particulate matter being removed in the filter. Each unit is supported on an inverted T-bar type ceiling gridwork. This type of unit is referred to herein as an individual plenum unit because each filter has its own plenum.
Another type of clean room construction involves supporting a plurality of high-efficiency filters within a gridwork suspended above the work area in the clean room and below the true ceiling of the room such that the filter gridwork extends between the four sidewalls of the room. The area between the filter gridwork and the true ceiling comprises a common plenum into which air is pumped for filtration downwardly through the filters. This second type of construction will be called common plenum construction because a plurality of filters share the same plenum.
The filters employed in either type of construction are HEPA filters. These filters ordinarily have particulate efficiencies exceeding 99.97% for 0.3 micron diameter particles as determined by the Army Chemical Corps D.O.P. test.
The individual filters, regardless of the type of system employed, must be sealed to the surrounding structure to prevent unfiltered air from short-circuiting from the plenum, common or individual, directly into the room. This is typically accomplished by running a bead of silicone caulk or similar material between the filter frame at the room-facing surface thereof and the surrounding support structure. Because of the relatively high pressures involved and the desirability of preventing any possible leakage, the sealant material is applied liberally in such fashion that it extends upwardly between the filter frame and the surrounding structure a substantial distance.
When it becomes necessary to replace the filter, the sealant material must be cut or otherwise fractured to permit removal of the filter from the surrounding structure. This has been accomplished in the past, typically, by use of a putty knife or similar tool which has been forced by hand between and around the filter frame and surrounding structure. This, as will be readily appreciated by those skilled in the art, is a most time-consuming and unpleasant task.
Therefore, there is a need for a clean room air diffuser filter unit which can be quickly and easily replaced, even by an unskilled worker. Furthermore, such a unit must have a complete, effective seal to prevent the short-circuiting of contaminants around the filter. Finally, the unit must be economical to manufacture.
The present invention is adapted for use in conjunction with a filter unit having a frame therearound and a supporting frame within which the filter unit is positioned, the peripheral area between the filter frame and support frame being sealed by a cuttable seal such as a silicone-based caulk to prevent air from short-circuiting between the filter frame and the support frame. It comprises an elongated, flexible cutting member such as a braided wire having one end thereof secured to the filter frame or support frame on one side of the cuttable seal, having the other end thereof exposed and grasped at the other side of the cuttable seal and having the intermediate length thereof positioned about the periphery of the filter frame on the said one side of the cuttable seal. When it is desired to remove the filter unit from the support frame, the exposed end of the cutting member is grasped and pulled progressively, causing the intermediate length to cut through the seal about the periphery of the filter frame.